IC Voltage Regulator
IC Voltage Regulator uses integrated circuits for voltage regulation . One advantage of IC voltage regulator is that properties like thermal compensation, short circuit protection and surge protection can be built into the device. Most of the commonly used IC voltage regulators are three-terminal devices.
Schematic Symbol for a Three-terminal IC Voltage Regulator
The figure below shows the schematic symbol for a three-terminal IC voltage regulator .
Types of IC Voltage Regulators
There are basically four types of IC voltage regulators :
- Fixed positive voltage regulator
- Fixed negative voltage regulator
- Adjustable voltage regulator
- Dual-tracking voltage regulator
Fixed Positive Voltage Regulator
This IC regulator provides a fixed positive output voltage. Although many types of IC regulators are available, the 7800 series of IC regulators is the most popular. The last two digits in the part number indicate the d.c. output voltage. For example [See Table below], the 7812 is a + 12V regulator whereas the 7805 is a + 5V regulator. Note that this series (7800 series) provides fixed regulated voltages from + 5 V to + 24V.
Circuit Diagram of Fixed Positive Voltage Regulator
The figure above shows the circuit diagram of fixed positive voltage regulator . You can see how the 7812 IC is connected to provide a fixed d.c. output of + 12V. The unregulated input voltage Vi is connected to the IC’s IN terminal and the IC’s OUT terminal provides + 12V. Capacitors, although not always necessary, are sometimes used on the input and output. The output capacitor (C2) acts basically as a line filter to improve transient response. The input capacitor (C1) is used to prevent unwanted oscillations.
Fixed Negative Voltage Regulator
This IC regulator provides a fixed negative ouput voltage. The 7900 series of IC regulators is commonly used for this purpose. This series (7900) is the negative-voltage counterpart of the7800 series [See Table below]. Note that 7900 series provides fixed regulated voltages from – 5V to – 24 V.
Circuit Diagram of Fixed Negative Voltage Regulator
You can see the circuit diagram of fixed negative voltage regulator below .
You can see how 7912 IC is connected to provide a fixed d.c. output of – 12 V. The unregulated negative input voltage Vi is connected to IC’s IN terminal and the IC’s OUT terminal provides – 12 V. Capacitors used in the circuit perform the same function as in a fixed positive regulator.
Adjustable Voltage Regulator
The adjustable voltage regulator can be adjusted to provide any d.c. output voltage that is within its two specified limits. The most popular three-terminal IC adjustable voltage regulator is the LM 317.
Circuit Diagram of Adjustable Voltage Regulator
The LM 317 is a three-terminal positive adjustable voltage regulator and can supply 1.5 A of load current over an adjustable output range of 1.25V to 37V. The figure above shows an unregulated power supply driving an LM 317 circuit. The data sheet of an LM 317 gives the following formula for the output voltage :
This formula is valid from 1.25 V to 37V.
Dual Tracking Voltage Regulator
The dual-tracking regulator provides equal positive and negative output voltages. This regulator is used when split-supply voltages are needed.
Circuit Diagram of Dual Tracking Voltage Regulator
The RC 4195 IC provides d.c. outputs of + 15V and – 15V. The device needs two unregulated input voltages. The positive input may be from + 18V to + 30V and the negative input from – 18V to –30V. As shown, the two outputs are ± 15V. The data sheet of an RC 4195 lists a maximum output current of 150 mA for each supply and a load regulation of 3mV. Adjustable dual-tracking regulators are also available. These regulators have outputs that can be varied between their two rated limits.
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